For the gnocchi: Stick the sweet potato a few times with a fork, wrap in a damp paper towel, and microwave until soft, about 7 minutes. (You can also bake the sweet potato in the oven, which will take closer to an hour.)

Scoop the flesh of the sweet potato into a mixing bowl. Discard the skin. Mix the ricotta, parmesan, and salt until well combined and almost completely smooth. Add the flour ½ cup at a time, kneading very gently after each addition (don’t over knead it - you don’t want it to get tough).

Eventually, as the dough becomes easier to handle, transfer it to a clean floured work surface and form it into a loaf, about 9x5 inches. Cut a slice off of the loaf on the short side (think of it as if it were a loaf of banana bread and you were going to cut a slice to eat). Roll and stretch the slice on a floured surface until it forms a long, skinny rope-like shape. Cut the rope into 1-inch segments and transfer to a bowl: this is your gnocchi.

Bring a large pot of water to boil, add the gnocchi, and boil until the gnocchi rise to the top of the water. Drain and toss gently with a little olive oil to prevent sticking. At this point you can make the rest of the recipe with the gnocchi, refrigerate the gnocchi to finish them later, or freeze them.

For the Broccoli Rabe: Bring a large pot of water to boil and prepare a bowl with ice water. Add the broccoli rabe to the boiling water and cook for 1 minute. Drain and transfer to the ice water to cool and stop the broccoli rabe from cooking further. Drain again and set aside.

Putting it all together: Heat the butter in a large skillet over medium high heat until lightly bubbling and foaming. Add the gnocchi and pan-fry until golden brown on the outside (you may have to do this in batches). Once the gnocchi is done, add the broccoli rabe, garlic, sage, and salt and pan-fry for another few minutes (again, working in batches). Remove from heat and let cool slightly so the butter thickens just a little. Add the cream to the pan along with the Parmesan cheese - toss gently a few times to combine (the sauce should coat the gnocchi and broccoli rabe very lightly) and serve immediately with salt, pepper, and a squeeze of lemon juice if you want.